Mammary tissue differentiation and tumorigenesis were
studied in female rats following subcutaneous injection at 2, 4 and 6 days
after birth with low or high doses of 17β-estradiol (0.1
or 10 µg; E2), biochanin A (0.1 or
10 mg; BCA) or bisphenol A (0.1 or 10.0 mg; BPA). Half of the rats were killed on day 35 to analyze the
terminal end bud (TEB), terminal duct (TD) and alveolar bud (AB) of the mammary
tissue. The remaining rats were injected, ip, with a dose of 50 mg/kg of
N-nitroso-N-methylurea (MNU) at 7 weeks of age and sacrificed 26 weeks later.
The incidence and multiplicity of mammary tumors (MT) decreased among all three
different treated groups, dose-dependently. However, the pattern of mammary
gland differentiation varied. No significant difference was observed after E2 administration.
TEB decreased dose-dependently in BCA treated groups and the number of TD and
AB were suppressed significantly in BPA high dose group.

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